Federal regulators are giving themselves an extra four months to perform a surprise do-or-die inspection of Parkland Memorial Hospital.

Under the original safety oversight agreement with the public hospital, struck in late 2011, Parkland was supposed to undergo such a survey some time before April 30, 2013.

It could still happen any day now. But regulators recently realized that not enough time was built into the agreement to allow for the element of surprise, said David Wright, deputy regional administrator for the U.S. Centers for Medicare & Medicaid Services.

“We need that final act [inspection] of the process to be shrouded in mystery so we have the most accurate view of the progress possible,” he said. Extending the time frame to late August makes it much more difficult for Parkland to predict when the survey will occur.

Parkland stands to lose hundreds of millions in annual federal funds vital to its survival if it doesn’t pass the survey, which could take up to two weeks to complete, CMS has warned.

Last week, I reported that Parkland has implemented 471 of 499 safety mandates. But the hospital is still grappling with correcting many problems such as unsanitary conditions, inconsistent doctor coverage for psychiatric patients and delays in efficiently moving patients through the hospital. The federal overseers said Parkland isn’t yet ready for an inspection.

Parkland is the largest hospital in the nation ever to operate under the oversight of federally installed safety monitors. That program is still highly experimental, and modifications to the agreement have to be made along the way to preserve the intent and integrity of the process, Wright said.

“Everyone is better served, including the community, to make sure we have enough time to go in and do a thorough investigation,’’ Wright said.

Parkland officials, who signed off on the agreement modification Tuesday, released a statement this morning saying, “The amendment allows CMS the element of surprise for its survey which is appropriate …Parkland should be ready for that level of scrutiny on any day at any hour.”

Early this afternoon, Parkland Memorial Hospital officials announced that they will place their troubled psychiatric services under the management of privately owned Green Oaks Hospital in Dallas.

News of the $1.1 million annual deal, posted on the hospital’s web site, is the culmination of confidential talks since November between the two parties. It marks a potentially significant shift for Parkland amid ongoing warnings from federal safety monitors that it needs to find a solution to persistent threats to psych patients.

The media statement said Parkland’s board of managers approved the deal — with member Dr. Winfred Parnell abstaining — during a Wednesday night meeting. Prior to the meeting, the hospital didn’t follow its usual practice of posting an advance meeting agenda and information packet on its website alerting the public.

Green Oaks, owned by Nashville, Tenn.-based HCA, provides a range of mental-health care from inpatient to ER services at its site near the Medical City Dallas Hospital campus. It also runs outpatient clinics or other facilities in Dallas, McKinney, Plano and Irving.

At Parkland, Green Oaks will provide an administrative director, nursing director, performance improvement director and a community liaison for psychiatric services, the statement said. Joe Householder, a spokesman for Parkland, told me that the deal “in no way alters the relationship/contract with” UT Southwestern Medical Center. UTSW, Parkland’s academic affiliate, is paid to supply faculty physicians to provide clinical care.